1. Field of the Invention
The present invention relates to a flow rate detecting element used in a thermosensitive flow rate sensor which measures the flow rate of a fluid. The present invention also relates to an element holder which accommodates the flow rate detecting element when the flow rate detecting element is put into practical use.
The flow rate detecting element of the present invention can be used for measuring the flow rate of various fluids such as gases and/or liquids, preferably gases, and particularly air and/or a mixture of gases. The flow rate detecting element of the present invention can be preferably used for measuring the flow rate of, in particular, the air intake into an internal combustion engine.
2. Description of the Related Art
The applicant of this patent application has filed an application for patent (Japanese Patent Kokai Publication No. 11-23338) related to a thermosensitive flow rate detecting element based on an operating principle similar to that of the present invention. FIG. 9(a) shows a schematic plan view of a key portion in a basic embodiment of the invention of the above Japanese Patent Kokai Publication, and FIG. 9(b) shows a schematic sectional view taken along lines IXBxe2x80x94IXB in FIG. 9(a).
In FIG. 9, reference numeral 31 denotes a flat substrate made of a silicon semiconductor, 32 denotes an insulating support film made of silicon nitride, 34, 35, 36 and 37 denote thermosensitive resistors made of, for example, platinum, where 34 is a heating resistance section, 35 and 36 are temperature detecting resistance sections and 37 is a comparative resistance section, and 33 denotes an insulating protective film made of silicon nitride.
As shown in FIG. 9(b), the flat substrate 31 has a recess 38 in the right-hand portion thereof, formed by removing a part of the substrate in a predetermined size and shape by etching or other method. The flat substrate 31 also has a notch 39 in the left-hand portion thereof, formed by removing a part of the substrate in a predetermined size and shape by etching or other method, so that the notch 39 having a cross section of substantially triangular shape with the base thereof lying at the lower surface of the substrate 31 does not reach the upper surface of the substrate 31. The terms xe2x80x9clower surfacexe2x80x9d and xe2x80x9cupper surfacexe2x80x9d are used herein in correspondence to the lower and upper positions in the drawings which show the longitudinal sectional view of the flow rate detecting element of the present invention, for the convenience of description.
On the upper surface of the flat substrate 31, the support film 32 and the protective film 33 are sequentially laminated. Provided between the support film 32 and the protective film 33 are the heating resistance section 34, the temperature detecting resistance sections 35, 36, and the comparative resistance section 37 being formed in predetermined patterns as shown in FIG. 9(a). A portion enclosed by two-dot and a dash line in FIG. 9(a), which includes the heating resistance section 34 and the temperature detecting resistance sections 35, 36 that are provided on both sides of the heating resistance section 34, constitutes a heating resistance region section 40. The heating resistance region 40 consists of a thin film comprising the support film 32 and the protective film 33 placed one on another, and constitutes a so-called diaphragm structure with the recess 38 formed on the bottom side so as not to contact the flat substrate 31.
Formed in the flat substrate 31 on the lower surface side of the comparative resistance section 37 is the notch 39 which opens only on the lower surface of the flat substrate 31. A portion of the flat substrate 31 remains on the side which is in contact with the support film 32.
In use condition of the flow rate detecting element having the constitution described above, the resistance sections 34, 35, 36 and 37 are connected to circuits not shown. When a fluid, for example air, flows in the direction indicated by arrow 50, the comparative resistance section 37 contacts with the flowing air via the protective film 33 to sense the temperature of the air. The temperature of the heating resistance section 34 is set to remain higher than the temperature being measured at the comparative resistance section 37 by a predetermined margin. For the application to an internal combustion engine of automobile, for example, temperature of the heating resistance section 34 is controlled to maintain a level 200 degree centigrade higher than the temperature being measured at the comparative resistance section 37.
Heat generated by the heating resistance section 34 is transmitted to the temperature detecting resistance sections 35, 36 via the support film 32 and the protective film 33. Since the temperature detecting resistance section 35 and the temperature detecting resistance section 36 are disposed at positions symmetrical with respect to the heating resistance section 34 which is located at the center as shown in FIG. 9, there is no difference in the resistance between the temperature detecting resistance section 35 and the temperature detecting resistance section 36 when there is no fluid flow. Also since the comparative resistance section 37 is located at a predetermined distance from the heating resistance section 34, heat generated by the heating resistance section 34 is substantially not transmitted to the comparative resistance section 37, so that the temperature of the comparative resistance section 37 is nearly equal to the temperature of the surrounding fluid, for example air.
When a fluid, for example air, flows in the direction indicated by the arrow 50 over the flow rate detecting element having such a constitution as described above, since the temperature of the heating resistance section 34 is set to a level generally higher than the fluid temperature to be measured, the temperature detecting resistance section 35 located in the upstream is cooled by the fluid to a lower its temperature. The temperature detecting resistance section 36 located in the downstream, on the other hand, receives the heat generated by the heating resistance section 34 and conveyed by the fluid, and therefore shows either a less drop in the temperature or a rise in the temperature. As a result, when the fluid flows in the direction indicated by the arrow 50, temperature of the temperature detecting resistance section 35 located in the upstream becomes lower than that of the temperature detecting resistance section 36 located in the downstream, while the difference in the resistance between the two temperature detecting resistance sections 35 and 36 becomes larger as the flow rate or the velocity of the fluid increases. Thus the flow rate or the velocity of the fluid can be measured by sensing the difference in the resistance between the temperature detecting resistance section 35 and the temperature detecting resistance section 36.
When the fluid flows in a direction opposite to the arrow 50, since the temperature of the temperature detecting resistance section 36 located in the upstream becomes lower than that of the temperature detecting resistance section 35 located in the downstream, contrary to the case described above, direction of the fluid flow can also be determined.
The thermosensitive flow rate detecting element as described above is accommodated in an element holder when it is practically used, in order to avoid the turbulence of the fluid flow and to achieve an effective contact of the fluid with the heating resistance section or the comparative resistance section. The applicant of this patent application has also filed an application for patent (Japanese Patent Kokai Publication No. 10-293052) on the element holder.
The flow rate detecting element described above measures flow rate by means of the heat transmission phenomenon of the fluid. Therefore, an accurate monitoring of the fluid temperature is required in order to measure the flow rate accurately. That is, when the fluid temperature varies, the comparative resistance section 37 provided on the substrate is required to detect the change without delay. When measuring an amount of the flow rate of air intake into an internal combustion engine, for example, there may be such occasions while running as the intake air temperature indicates a sudden change at, for example, the entry and exit of a tunnel. To have the internal combustion engine operate with the best performance even in such cases, the air temperature change must be detected quickly and accurately. Consequently, the flow rate detecting element is required to have good response characteristics with respect to the intake air temperature.
Silicon has a relatively large thermal capacity. As a result, in case the substrate 31 made of silicon is provided under the comparative resistance section 37, the comparative resistance section 37 has greater apparent thermal capacity which results in a limitation to the improvement of the response characteristics of the flow rate detecting element with respect to the fluid temperature changes.
With the background described above, such an attempt has been made that introduces the diaphragm structure for the comparative resistance section 37 similarly to the heating resistance region 40. However, the comparative resistance section 37 is required to have even better temperature response characteristic which means that the time required to detect the fluid temperature change is desired to be as short as possible. Thus the comparative resistance section 37 is required to have even better temperature response characteristic even when the diaphragm structure is employed.
First object of the invention of the present application is to provide a flow rate detecting element having a comparative resistance section made in such a structure that has an improved temperature response characteristic, by placing emphasis particularly on the temperature response characteristic of the comparative resistance section in the thermosensitive flow rate detecting element described above.
Second object of the invention of the present application is to provide an element holder which accommodates the thermosensitive flow rate detecting element having the comparative resistance section made in such a structure that has an improved temperature response characteristic, when put in practical use.
The flow rate detecting element according to the first aspect of the present invention has a thin film layer comprising a support film and a protective film which are made of insulating material and are formed on one surface of a flat substrate, where a heating resistance section and a comparative resistance section are provided by disposing thermosensitive resistor in predetermined patterns between the support film and the protective film of the thin film layer, and the flat substrate has a recess which penetrates the flat substrate in the direction of thickness thereof in at least a part thereof that faces the heating resistance section and the comparative resistance section, so that the thermosensitive flow rate detecting element measures the flow rate or velocity of a fluid by means of the heating resistance section according to the report of fluid temperature sensed by the comparative resistance section, while a fluid flow passage is provided which communicates with the recess that faces the comparative resistance section thereby to cause the fluid to flow to the recess.
The flow rate detecting element constituted as described above makes it possible to bring the fluid into sufficient contact also with the lower surface of the comparative resistance section having the diaphragm structure, by the fluid flow passage communicating with the recess that faces the comparative resistance section and flowing the fluid smoothly through the fluid flow passage into the recess. Thus since the comparative resistance section of the flow rate detecting element can make contact with the fluid on both the upper surface and the lower surface thereof and the fluid which contacts the lower surface also flows quickly through the fluid flow passage, the fluid temperature can be sensed sensitively. As a result, the flow rate detecting element can make quick response to the temperature change even when the fluid temperature changes suddenly.
The flow rate detecting element according to the second aspect of the present application is a variation of the flow rate detecting element of the first aspect, wherein at least two fluid flow passages are provided.
In the flow rate detecting element constituted as described above, the fluid can be caused to flow more smoothly into the recess by arranging at least one of the fluid flow passages at an fluid inlet-side of the recess and at least one of the fluid flow passages at an fluid outlet-side of the recess. Therefore, the comparative resistance section of the flow rate detecting element can sense the fluid temperature accurately, and the flow rate detecting element can make quick response to the temperature change even when the fluid temperature changes suddenly.
The flow rate detecting element according to the third aspect of the present application is a variation of the flow rate detecting element of the first aspect, wherein at least one fluid flow passage is provided in the upstream of the comparative resistance section in the main flow direction of the fluid to be measured.
In the flow rate detecting element constituted as described above, the fluid is made easier to flow through the fluid flow passage into the recess so that the fluid can flow more smoothly into the recess by providing at least one fluid flow passage in the upstream of the comparative resistance section in the main flow direction of the fluid to be measured. Therefore, the comparative resistance section of the flow rate detecting element can sense the fluid temperature sensitively, and the flow rate detecting element can make quick response to the temperature change even when the fluid temperature changes suddenly.
The flow rate detecting element according to the fourth aspect of the present application is a variation of the flow rate detecting element of the first aspect, wherein at least one fluid flow passage is provided in the downstream of the comparative resistance section in the main flow direction of the fluid to be measured.
In the flow rate detecting element constituted as described above, the fluid is made easier to flow through the fluid flow passage into the recess so that the fluid can flow more smoothly into the recess, by providing at least one fluid flow passage in the downstream of the comparative resistance section in the main flow direction of the fluid to be measured. Therefore, the comparative resistance section of the flow rate detecting element can sense the fluid temperature sensitively, and the flow rate detecting element can make quick response to the temperature change even when the fluid temperature changes suddenly.
The flow rate detecting element according to the fifth aspect of the present invention is a variation of the flow rate detecting element of the first aspect, wherein the comparative resistance section and the heating resistance section are disposed on a line which crosses the direction of the main flow direction of the fluid to be measured.
In the flow rate detecting element constituted as described above, the comparative resistance section and the heating resistance section are disposed on the line which crosses the direction of the main flow of the fluid to be measured. Accordingly, the fluid can be prevented from making contact with the heating resistance section after making contact with the comparative resistance section or from making contact with the comparative resistance section after making contact with the heating resistance section, thereby preventing the comparative resistance section and the heating resistance section from giving thermal influence to each other. As a result, the comparative resistance section of the flow rate detecting element can sense the fluid temperature more accurately without being affected by the heating resistance section. Also the heating resistance section can sense the temperature change due to the interaction with the fluid more accurately without being affected by the comparative resistance section.
The flow rate detecting element according to the sixth aspect of the present application is a variation of the flow rate detecting element of the first aspect, wherein the comparative resistance section and the heating resistance section are disposed on a line which crosses the direction of the main flow of the fluid to be measured at right angles.
In the flow rate detecting element constituted as described above, the comparative resistance section and the heating resistance section are disposed on the line which crosses the direction of the main flow of the fluid to be measured at right angles. Accordingly, the fluid can be prevented from making contact with the heating resistance section after making contact with the comparative resistance section or from making contact with the comparative resistance section after making contact with the heating resistance section, thereby preventing the comparative resistance section and the heating resistance section from giving thermal influence to each other. As a result, the comparative resistance section of the flow rate detecting element can sense the fluid temperature more accurately without being affected by the heating resistance section. Also the heating resistance section can sense the temperature change due to the interaction with the fluid without being affected by the comparative resistance section.
The seventh aspect of the present invention provides a thermosensitive flow rate detecting element which has a thin film layer comprising a support film and a protective film, both made of insulating material and formed on one surface of a flat substrate, where a heating resistance section and a comparative resistance section are provided by disposing thermosensitive resistor in predetermined patterns between the support film and the protective film of the thin film layer, and the flat substrate has a recess which penetrates the flat substrate in the direction of thickness thereof provided in at least portions thereof that face the heating resistance section and the comparative resistance section, so that the thermosensitive flow rate detecting element measures the flow rate or velocity of a fluid by means of the heating resistance section according to the report of fluid temperature sensed by the comparative resistance section, while at least two fluid flow passages are provided which communicates with the recess that faces the comparative resistance section to cause the fluid to flow to the recess, with the fluid flow passage being of one type selected from among the group consisting of:
(i) a hole which penetrates the thin film layer in the direction of thickness thereof to flow the fluid across the thin film layer between the upper surface and the lower surface thereof;
(ii) at least one groove which communicate between a recess wall surface facing the comparative resistance section and one end wall surface of the substrate on the surface of the substrate opposite to the thin film layer; and
(iii) at least one tubular passage which communicates between the recess wall surface facing the comparative resistance section and one end wall surface of the substrate.
In the flow rate detecting element constituted as described above, as the first feature, the fluid can be caused to flow more smoothly into the recess by providing at least two fluid flow passages which communicate the recess facing the comparative resistance section to flow the fluid to the recess, while arranging at least one of the fluid flow passages at an fluid inlet-side of the recess and at least one of the fluid flow passages at an fluid outlet-side of the recess. Therefore, the comparative resistance section of the flow rate detecting element can sense the fluid temperature accurately, and the flow rate detecting element can make quick response to the temperature change even when the fluid temperature changes suddenly.
In the flow rate detecting element constituted as described above, as the second feature, a smooth passage can be provided for the fluid to flow through the fluid flow passages to the recess by using at least one type of flow passage selected from among a group of (i) hole, (ii) groove and (iii) tubular passage as the fluid flow passages.
The flow rate detecting element according to the eighth aspect of the present application is a variation of the flow rate detecting element of the seventh aspect, wherein the fluid flow passage provided in the upstream is a hole which penetrates the thin film layer in the direction of thickness thereof to let the fluid flow between the upper surface and the lower surface of the thin film layer, and the fluid flow passage provided in the downstream is a passage of at least one type selected from among a group consisting of:
(i) a hole which penetrates the thin film layer in the direction of thickness thereof to flow the fluid across the thin film layer between the upper surface and the lower surface thereof;
(ii) at least one groove which communicates between a recess wall surface facing the comparative resistance section and one end wall surface of the substrate on the surface of the substrate opposite to the thin film layer; and
(iii) at least one tubular passage which communicates between a recessed wall surface facing the comparative resistance section and one end wall surface of the substrate.
In the flow rate detecting element constituted as described above, since the hole is used as the fluid flow passage provided in the upstream and a flow passage of at least one type selected from hole, groove and tubular passage is used as the fluid flow passage provided in the downstream, the fluid can flow through the hole located in the upstream into the recess and flow out of the recess through the fluid flow passage of at least one type selected from hole, groove and tubular passage, thus securing a smooth passage for the fluid to flow into the recess. As a result, the comparative resistance section has an improved temperature response characteristic as the fluid can flow sufficiently also to the lower surface of the comparative resistance section.
The flow rate detecting element according to the ninth aspect of the present application is a variation of the flow rate detecting element of the eighth aspect, wherein a fluid flow passage having a form of slit is provided in the upstream and the thin film layer is warped, at least in a part of the comparative resistance section, so as to be convex to the opposite side of the substrate.
In the flow rate detecting element constituted as described above, since the thin film layer is warped, at least in a part of the comparative resistance section, so as to be convex to the opposite side of the substrate, the fluid can flow more smoothly through the hole into the recess. As a result, the comparative resistance section has an improved temperature response characteristic since the fluid can flow more efficiently to the lower surface of the comparative resistance section.
The flow rate detecting element according to the tenth aspect of the present application is a variation of the flow rate detecting element of the ninth aspect, wherein a fluid flow passage having a form of slit is provided in the downstream.
In the flow rate detecting element constituted as described above, since both fluid flow passages disposed in the upstream and the downstream are formed in slits and the thin film layer is warped, at least in a part of the comparative resistance section, so as to be convex to the opposite side of the substrate, the fluid can flow more smoothly through the slit into the recess. As a result, the comparative resistance section has an improved temperature response characteristic since the fluid can flow more efficiently to the lower surface of the comparative resistance section.
The flow rate detecting element according to the eleventh aspect of the present application is a variation of the flow rate detecting element of the seventh aspect, wherein at least one groove which communicates between the recess wall surface facing the comparative resistance section and one end wall surface of the substrate is provided on the surface of the substrate opposite to the thin film surface, as the fluid flow passage in the upstream, and the fluid flow passage provided in the downstream is a passage of at least one type selected from among a group consisting of:
(i) a hole which penetrates the thin film layer in the direction of thickness thereof to flow the fluid across the thin film layer between the upper surface and the lower surface thereof;
(ii) at least one groove which communicates between a recess wall surface facing the comparative resistance section and one end wall surface of the substrate on the surface of the substrate opposite to the thin film layer; and
(iii) at least one tubular passage which communicates between a recess wall surface facing the comparative resistance section and one end wall surface of the substrate.
In the flow rate detecting element constituted as described above, since the groove is used as the fluid flow passage provided in the upstream and a passage of at least one type selected from hole, groove and tubular passage is used as the fluid flow passage provided in the downstream, the fluid can flow through the groove located upstream into the recess and flow out of the recess through the fluid flow passage of at least one type selected from hole, groove and tubular passage located in the downstream, thus securing a smooth passage for the fluid to flow into the recess. As a result, the comparative resistance section has an improved temperature response characteristic since the fluid can flow sufficiently also to the lower surface of the comparative resistance section.
The flow rate detecting element according to the twelfth aspect of the present invention is a variation of the flow rate detecting element of the eleventh aspect, wherein the groove as the fluid flow passage is formed so that the sectional area thereof at the opening in the recess wall surface facing the comparative resistance section or in the end wall surface of the substrate is larger than the sectional area of any other portion of the groove.
In the flow rate detecting element constituted as described above, since the sectional area thereof at the opening in the recess wall surface facing the comparative resistance section or in the end wall surface of the substrate is larger than the sectional area of any other portion of the groove, the fluid is made easier to flow into the groove and flow out of the groove. As a result, the comparative resistance section has an improved temperature response characteristic since the fluid can flow also to the lower surface of the comparative resistance section more smoothly.
The flow rate detecting element according to the thirteenth aspect of the present invention is a variation of the flow rate detecting element of the seventh aspect, wherein at least one tubular passage which communicates between the recess wall surface facing the comparative resistance section and one end wall surface of the substrate is provided as the fluid flow passage in the upstream, and the fluid flow passage provided in the downstream is a passage of at least one type selected from among the group consisting of:
(i) a hole which penetrates the thin film layer in the direction of thickness thereof to flow the fluid across the thin film layer between the upper surface and the lower surface thereof;
(ii) at least one groove which communicates between a recess wall surface facing the comparative resistance section and one end wall surface of the substrate on the surface opposite to the thin film layer of the substrate; and
(iii) at least one tubular passage which communicates between a recess wall surface facing the comparative resistance section and one end wall surface of the substrate.
In the flow rate detecting element constituted as described above, since the tubular passage is used as the fluid flow passage provided in the upstream and a passage of at least one type selected from hole, groove and tubular passage is used as the fluid flow passage provided in the downstream, the fluid can flow through the tubular passage located in the upstream into the recess and flow out of the recess through the fluid flow passage of at least one type selected from hole, groove and tubular passage located in the downstream, thus securing a smooth passage for the fluid to flow into the recess. As a result, the comparative resistance section has an improved temperature response characteristic since the fluid can flow sufficiently also to the lower surface of the comparative resistance section.
The invention of element holder according to the first aspect of the present application provides an element holder for accommodating a thermosensitive flow rate detecting element which comprises a flat substrate having a thin film layer that consists of a support film and a protective film both made of insulating material and laminated on one surface thereof, wherein a heating resistance section and a comparative resistance section are provided between the support film and the protective film of the thin film layer by disposing thermosensitive resistor in predetermined patterns, the flat substrate has a recess which penetrates the flat substrate in the direction of thickness thereof in at least such portions thereof that face the heating resistance section and the comparative resistance section, and a fluid flow passage which communicates with the recess facing the comparative resistance section is provided to flow the fluid to the recess, so that the thermosensitive flow rate detecting element measures the flow rate or velocity of the fluid by means of the heating resistance section according to the report of fluid temperature sensed by the comparative resistance section, the element holder having airfoil-shaped cross section with at least one gap opening provided in the holder surface in the upstream and the downstream portions with respect to the comparative resistance section.
The element holder constituted as described above causes no significant disturbance to the fluid flow around the element holder because of the airfoil-shaped cross section, and rather shows flow straightening effect so that the fluid is introduced through the gap opening in the upstream of the comparative resistance section into the holder and, after making sufficient contact with the flow rate detecting element accommodated therein, particularly with the comparative resistance section, the fluid can be discharged to the outside of the holder through the gap opening located in the downstream of the comparative resistance section. Thus the fluid can sufficiently make contact with the flow rate detecting element accommodated therein. As a result, the comparative resistance section of the flow rate detecting element can exhibit good temperature response characteristic without substantially disturbing the fluid flow.
The invention of element holder according to the second aspect of the present application is the element holder of the first aspect, wherein the gap opening located in the upstream of the comparative resistance section is provided at a position which corresponds to the upper surface of the flow rate detecting element that is accommodated therein.
The element holder constituted as described above, when used in conjunction with the flow rate detecting element which has a hole provided as the fluid flow passage in the upstream of the flow rate detecting element, the gap opening located in the upstream of the element holder and the hole provided as the fluid flow passage of the flow rate detecting element accommodated therein can be disposed so as to oppose each other. As a result, the fluid flow in the element holder and around the flow rate detecting element can be made smoother.
The invention of element holder according to the third aspect of the present application is the element holder of the first aspect, wherein the lower edge of the gap opening located in the upstream of the comparative resistance section is provided at a position which corresponds to the end wall surface of the substrate of the flow rate detecting element that is accommodated therein.
The element holder constituted as described above, when used in conjunction with the flow rate detecting element which has a tubular passage that opens in the end wall surface located in the upstream of the substrate, the gap opening located in the upstream of the element holder and the tubular passage provided as the fluid flow passage of the flow rate detecting element accommodated therein can be disposed so as to oppose each other. As a result, the fluid flow in the element holder and around the flow rate detecting element can be made smoother.
The invention of element holder according to the fourth aspect of the present application is the element holder of the first aspect, wherein the lower edge of the gap opening located in the upstream of the comparative resistance section is provided at a position the same level as or lower than the lower surface of the substrate or at a position below thereof in the flow rate detecting element that is accommodated therein.
The element holder constituted as described above, when used in conjunction with the flow rate detecting element which has a groove provided in the lower surface of the substrate as the fluid flow passage located in the upstream of the flow rate detecting element, makes it possible to dispose the gap opening located in the upstream of the element holder and the groove provided as the fluid flow passage of the flow rate detecting element accommodated therein so as to oppose each other. As a result, the fluid flow in the element holder and around the flow rate detecting element can be made smoother.